First-principles simulations of ferroelectric oxides

Problematics, choice of adequate calculational scheme and obtained results in the first-principles simulations of potassium niobate (in different ferr oelectric phases), pure and Li-doped potassium tantalate, and lithium nioba te are discussed. The ferroelectric instability zone-center TO phonons, and crystallographic as well as optical characteristics of defects are concent rated on. For intrinsic defects, F centers (associated with O vacancies) an d bound hole polarons (trapped by K vacancies) in KNbO3 are discussed. In L i-doped KTaO3, the interaction energies between substitutional impurities a t adjacent K sites, which undergo different patterns of off-center displace ments, are estimated. For LiNbO3, the frequencies and eigenvectors of Gamma TO phonons in all symmetry modes have been calculated.